Ni-based alloy improved in oxidation-resistance, high temperature strength and hot workability

Abstract

A nickel-based alloy is provided for provide parts and members of improved oxidation-resistance and high temperature strength for use in an oxidation atmosphere at high temperatures, such as automobile parts including an electrode for an ignition plug, power plant facility parts including a gas turbine nozzle, inner parts of heat treat furnaces, and fuel cell parts. The alloy improved in oxidation-resistance, high temperature strength and hot workability consists essentially of, in mass percentage, C: 0.003 to 0.1%, Si: 1.0% or less, Mn: 2.0% or less, Cr: 12 to 32%, Fe: 20% or less, Mg: 0.001 to 0.04%, at least one element, of not more than 2.5% in total, selected from the group consisting of Nb, Ta and V, impurity elements of S: 0.01% or less, but the ratio of the Mg-content to the S-content (Mg / S) being 1 or more, and Ti: 0 inclusive to 0.02%, and the rest being Ni and incidental impurities.

Description

BACKGROUND OF THE INVENTION1. Field of the InventionThe present invention relates to a Ni-based alloy improved in oxidation-resistance, high temperature strength and hot workability, which alloy is suitable for making parts and members used at high temperatures exposed to an oxidation atmosphere, including automobile parts such as ignition plug electrodes, power plant facility's parts such as gas turbine nozzles, inner parts of heat treatment furnaces, and fuel cell's parts.2. Description of the Related ArtConventionally, a Ni-18Cr-7Fe alloy (Alloy 600), which has a high oxidation-resistance, has been used for parts which are exposed in an oxidation atmosphere at high temperatures. Oxidation-resistance of a material is required to prevent volume loss or embrittlement of the material due to oxidation while being used at high temperature in air or gas atmosphere. The oxidation-resistance of Alloy 600 is maintained because a Cr2O3 layer is formed on its surface at a high temperature th...

AI Technical Summary

Benefits of technology

The object of the present invention is to provide parts and members improved in oxidation-resistance, high temperature strength and hot workability for use in an oxidation atmosphere at high temperatures, including automobile parts such as an ignition plug electrodes, power plant's facility parts such as gas turbine nozzles, inner parts of heat treatment furnaces, and fuel cell's parts.

The inventors of the present invention studied the above described problem of the high temperature strength and consequently have found that adding a small amount of one or more of Nb, Ta and V prevents the coarsening of austenite grains during hot working and heat treatment thus achieving fine austenite grains, and thereby strength deterioration during use at high temperatures is successfully suppressed.

However, containing one or more of Nb, Ta and V causes an increase in resistance to deformation of the matrix compared to a Ni-based alloy that does not contain these elements, and thus deterioration of strength of the grain boundaries easily results in surface cracks or fracture occurrence. Then the present inventors investigated the issue of hot workability and have found that to achieve an alloy free from defects such as surface cracks or fracture, it is essential to add Mg which serves effectively to improve hot workability due to the resultant, strong grain boundaries.

Furthermore, utilization of the precipitation hardening mechanism is contemplated to maintain a high temperature strength. Thus, it was found that adding Al that is a precipitation strengthening element in Ni-based alloys to an alloy containing at least one of Nb, Ta and V and added with Mg further improves the oxidation-resistance.

Thus, the present invention is a Ni-based alloy having improved oxidation-resistance, high temperature strength and hot workability, consisting essentially of, in mass percentage, C: 0.003 to 0.1%, Si: 1.0% or less, Mn: 2.0% or less, Cr: 12 to 32%, Fe: 20% or less, Mg: 0.001 to 0.04%, at least one element, of not more than 2.5% in total, selected from the group consisting of Nb, Ta and V, impurity elements of S: 0.01% or less, but the ratio of the Mg-content to the S-content (Mg / S) being 1 or more, and Ti: 0 inclusive to 0.02%, and the rest being Ni and incidental impurities.

The present invention is a Ni-based alloy improved in oxidation-resistance, high temperature strength and hot workability wherein average diameters of circle equivalent to particle of compounds of Nb, Ta or V are preferably not more than 2.0 μm.

Problems solved by technology

However, containing one or more of Nb, Ta and V causes an increase in resistance to deformation of the matrix compared to a Ni-based alloy that does not contain these elements, and thus deterioration of strength of the grain boundaries easily results in surface cracks or fracture occurrence.

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